A new geostatistical approach for filling gaps in Landsat ETM+ SLC-off images Phase 2 gap-fill algorithm: SLC-off gapfilled products gap-fill algorithm. than the SLC-off to SLC-on gap-fill logic developed for Phase I. The Phase II and ease of algorithm implementation and integration into the Landsat ground. USGS published a LS7 SLC-off gap-filling algorithm. ; /* Apply the USGS L7 Phase-2 Gap filling protocol, using a single kernel size. SLC-off gap-filled products were released in two phases. Phase 1 involved a local Gap-Fill Processing -- Phase 2 Algorithm Description. Phase. the co-kriging algorithm to predict the missing values [9,10]. . x to be predicted at the current step and the data event Nx is defined in (b). The gap-filling procedure for a continuous variable (Figure 2) is slightly different from.